I'd say there's plenty of in universe reasons to believe that an alternative plan would have been viable by virtue of Venat deliberately going out of her way to avoid informing the Ancients of what was coming. Had they been made aware of the impending arrival of the Final Days as well as Meteion's existence then there's ample reason to believe that they would have fought tooth and nail in order to survive.

The game also makes it pretty clear that the Sundered aren't going to just roll over and die whenever they're faced with a seemingly unstoppable force so there's no reason to assume that the Ancients 'needed' to just allow themselves to be subjected to genocide at the behest of a pair of deluded nutters in the form of Hermes and Venat.

To say nothing of the simple fact that the writers themselves have remained cautious to word things in such a way as for Venat's belief of the Ancient's supposed 'dead end' to be just that - a belief rather than a certainty.

All of which has, of course, been outlined and pointed out a great many times throughout this thread by this point.